When I watch a video like MKBHD (in 4K, but 21:9 aspect ratio), the image gets vertically compressed by maybe 10%. This is happening on my 2017 Philips 7272 TV with Oreo and the latest YouTube app. If I manually switch to 1440p or below, the issue does not appear. If I switch back to 4K after having first reduced the resolution, the image retains the right aspect ratio for a short while before being vertically compressed again (possibly once the resolution actually changes back up to 4K).

Does anyone else experience something similar? Does anyone have an idea of how to fix this?